This invention relates generally to remote terminal service in which a client computer functions as a remote terminal for a server computer, and more particularly to the display of graphic user interface by the client computer in a remote terminal session.
Before the advent of personal computers, large, expensive, mainframe computers dominated the landscape of digital computing. Each mainframe computer typically served multiple users that interfaced with the mainframe computer through terminals that had a display device, such as a cathode-ray tube (CRT) screen, and an input device, such as a keyboard. Such terminals are nowadays commonly referred to as xe2x80x9cdumb terminalsxe2x80x9d because they performed only basic display and input functions and had at most some rudimental digital processing capability that was not sufficient for independently running software applications.
The display provided by the xe2x80x9cdumbxe2x80x9d terminals was character-based, i.e., the display comprised alphanumeric letters. During operation, the user input entered through the keyboard is transmitted to the mainframe computer, and the output in the form of letters and numbers was sent to the terminal and displayed on its screen for viewing by the user.
In the beginning of the age of personal computers, personal computers were small machines with limited computing power and resources. They typically operated as individual units in the sense that each computer had its own operating system, ran its own software applications, received user input from its own input devices, and sent the user interface to its own CRT for display. In the early days, the PC interface was, like the dumb terminals for mainframes, based on alphanumeric characters. Graphic user interface, however, soon replaced the character-based display and became the norm for software applications designed to run on personal computers and networks based on personal computers.
Over time, the computing power of personal computers in terms of both hardware capabilities and software sophistication has increased tremendously. Many personal computers nowadays possess computing power and resources rivaling some small mainframe computers in the past. At the same time, networking of personal computers has become prevalent at workplaces. Due to these developments, there arises the possibility to run a software application on a server computer, which may be a network server, with the user running the application sitting at a remote client computer connected to the server computer through a network. In the capacity of a remote terminal, the client computer functions like a dumb terminal of the old days in that it forwards the user input to the server computer for processing and displays the user interface received from the server computer on its screen for viewing by the user. In a proposed scheme for remote terminal service, the client computer functions entirely in a slave mode in that the server computer tells the client computer exactly what to put on the user interface screen.
There are, however, many differences between a client computer functioning as a remote terminal and a dumb terminal of the past. One of the major differences is that the user interface has become much more sophisticated. A user interface screen on current personal computers is graphics-oriented and includes various graphic components such as text strings, icons, windows, etc. To enable the remote terminal to display the interface screen, the terminal server has to pass data regarding each graphic component, such as their bitmaps and coordinates, to the client computer. Because the remote terminal is connected to the server computer through a network, the data transmission can be quite time consuming, and the efficient use of the network bandwidth has to be considered in designing the remote terminal service system. If the amount of.graphics data that have to be sent to the remote terminal is large, the network data transmission can become a bottleneck and negatively impacts the display performance of the remote terminal.
The efficient use of network bandwidth in a remote terminal session is especially import for displaying characters. An interface screen may contain many text strings each having multiple characters. Generally, each character has a Unicode designation, and the graphics engine of the client computer can use the Unicode designation and the font information of a character to render it for display. Thus, the server computer may instruct the client computer to display a text string by sending only the Unicode designations and font of the characters in the string to the client computer. This approach, however, does not work in many cases. In the remote terminal server-client scheme, the server and the client may be on different operating system platforms, and the client may not even have the set of fonts that the server has. As a result, the same characters may be rendered differently by the different graphics engines, and the remote terminal may display characters in a form different from what is intended by the server. One solution to avoid this problem is to send glyphs for the characters to be displayed to the terminal client. Each glyph contains the bitmap representation of a character of a given font and size. Sending the glyphs across the network, however, can be quite expensive. A single glyph may be over 256 bytes long. When the user interface screen to be displayed at the remote terminal contains many characters, sending the glyphs to the terminal client may take up a significant portion of network bandwidth.
In view of the foregoing, the present invention provides a method and system of caching graphic representation data of glyphs to be displayed by a remote terminal that significantly reduces the amount of glyph data that have to be transmitted through the network.to the remote terminal. In accordance with the invention, the glyph data caching is performed on the level of xe2x80x9cfragments,xe2x80x9d each fragment containing a plurality of glyphs. A fragment may represent, for example, icon text, menu text, a text string in a document, etc., to be drawn on the remote terminal. In a typical remote terminal session, many fragments are drawn on the remote terminal multiple times due to screen refresh or other reasons, and caching those fragments avoids the need to resend all the glyph data for the fragments across the network to the remote terminal.
To provide fragment caching the terminal client stores a fragment cache for storing data representing fragments. The client also stores glyph caches for caching the bitmap representations of individual glyphs. The fragment cache and the glyph caches are maintained by a terminal server module of the server computer. Each entry in the fragment cache represents a fragment and contains data indicating where the glyph data for the glyphs in the fragment are stored in the glyph caches. When the remote terminal server receives a request to display a fragment on the remote terminal, it checks whether the fragment has been cached. If so, the terminal server sends the terminal client a fragment index that identifies the fragment cache entry for the fragment. The client then uses the data in that fragment cache entry to retrieve the data for the glyphs of the fragment from the glyph caches and render them on the display screen.
Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments, which proceeds with reference to the accompanying figures.